Recuperative heat exchanger and process of producing same



June 30, 1953 H. F. BUSCHOW RECUPERATIVE HEAT EXCHANGER AND PROCESS OF PRODUCING SAME Filed Sept. 9. 1948 2 Sheets-Sheet 1 INVENTOR. flrmdlt Ffiasrfiaal Q eedZ/w June 30, 1953 H. F. Bu'scHow RECUPERATIVE HEAT EXCHANGER AND PROCESS OF PRODUCING SAME 2 Sheets-$heet 2 Filed Sept. 9. 1948 kman F Bust/10w y @a'mgw adZ/u Patented June 30, 1953 RECUPERATIVE 2,643,363 w HEAT EXCHANGER AND PROCESS OF PRODUCING SAME Herman F. Buschow, North Arlington, N. J assignor to Hydrocarbon Research, Inc., New York, N. Y., a corporation of New Jersey Application September 9, 1948, Serial No. 48,508

the products of rectification on the one hand and the air on the other and for efiicient purging of the exchangers upon reversal of fiow there'- through to effect substantially complete removal from the exchangers of condensibles deposited therein from the air stream thereby permitting continuous operation.

Cold exchangers are well known in which the relatively warm incoming air and the relatively cold outgoing products of rectification are alternately passed with periodically reversed operation, so that streams of warm air are flowed through the same packing-filled spaces as the cold rectification products traversed during the preceding step of the process, the condensibles deposited in these'spaces during the passage of air therethrough being removed by sublimation and evaporation during the subsequent fiow therethrough of the products of rectification. To

provide for relatively high cold transfer efficiencies, cold exchangers heretofore employed have consisted of a cylindrical shell having therein a large number of tubes, each provided with an interior accordion-type fin of foil-like metal of high-heat conductivity disposed to form channels extending longitudinally through each tube and. a somewhat similar accordion-type fin on the exterior thereof. These fins are usually made by folding thin sheets of copper or aluminum into shape to produce the desired channels and then bonding them to the interior and exterior walls of the tubes by coating these walls with soldering metal, placing the fin sections folded in the desired shape in contact with the solder coating, then heating the assembly to a temperature so that the solder on the tube walls wets the fins and later cooling, thereby obtaining a bond between the tube Walls and the portion of the fins in contact therewith. This method of producing exchangers is arduous and timeconsuming and greatly increases the cost of the exchanger. I

In my copending application, Serial No. 678,464, filed June 21', 1946, now U. S. Patent 2,532,283

issued on December'S', 1950, there is disclosed an improved type of exchanger representing an important advance in the exchanger art, in which disc's,each 0f foil-like thickness, produceableby a simple stamping operation without waste of heat-conducting material are readily assembled by insertion on the inside 'or outside of each I tube in substantially abutting relationship, thus producing a multiplicity of longitudinally extending passages defined by the foil-like high heat conducting material of the discs deflected by the stamping operation to form the passages. The invention of this application is in the nature of an improvement on the invention disclosed and claimed in my aforesaid copending application, especially in that it eliminates the necessity for producing separate discs'and inserting them in each of the flow paths of the exchanger.

Among the'objects of this invention is to provide a novel method of producing an exchanger which materially. reduces the labor and time involved in forming such exchanger.

Another'object is to provide a cold exchanger having an exceptionally high area of cold exchanger surface per unit of volume and which can more readily be fabricated and assembled than heretofore known exchangers.

Still another object of the invention is to provide an exchanger so constructed and designed that each individual unit can be tested and evaluated to determine whether, in operation, satisfactory cold exchange will take place between the air and the products of rectification so that when such unit is assembled with other like unitsto form an exchanger of any desired capacity the resultant assembly will give the desired cold exchange between the air and the rectificationv products passed threthrough,

Other objectsand advantages Of this invention will be apparent from the following detailed description thereof. 7

In the accompanying drawings forming a part of this specification and showing for purposes of exemplification a preferred form of this invention without limiting the claimed invention to such illustrative instance:

Figure 1 is a diagrammatic perspectiveview illustrating the novel method of this invention for producing an exchanger unit also embodying this invention;

Figure 2 is a fragmentary plan view of a strip of high heat conducting material showing several stages of the manipulation of the strip to place it in form for winding on a tubular support; Y

Figure 3 is a vertical section taken in a plane passing through line 3-3 of Figure 2;

Figure 4 is a cross-section, normal to the direction of gas flow, through an exchanger unit embodying this invention;

Figure 5 is a fragmentary elevational view of an assembly of exchanger units embodying this invention; and

Figure 6 is a vertical section taken in a plane passing through the axis of one of the exchanger:- units shown in Figure 5 and at right angles to v the view of Figure 5.

The process of producing the exchanger unit of this invention involves rotating a supporting tube In, desirably with its axis positionediin-"a horizontal direction. For example, tube 10 maybe vanes in a single stamping operation rather than to produce such vanes step by step, as hereinabove described. Similarly, the equipment may be designed to operate continuously, i. e., the

- strip'may pass therethrough without interrupting held by a rotating brace, not shown, to ,efiect rotation of the tube. Tube i0 may be of aluminum, copper, or other high heat conducting material and may have on the circumferential sur- ,its movement during the stamping operation.

In the continued movement of the strip l5,

the ,strippasses through a crimping or corruface thereof alayer or -sheet' l -of-solder orof any well known brazing material, e. g., aluminumsilicon composition in the case where an aluminum strip hereinafter described iswound on an aluminum supporting tube l0.

'A carriage "I2 is mounted .for -movement on tracks l3 which extend in a direction parallel with the longitudinal axis of tube 10. Carriage I2 is driven by any suitable mechanism to effect movement thereof on tracks I3. Mounted-on carriage I2 is a roll ldcontaininga long ;thin flat strip or ribbon l5 of high heatconducting material, such, for example, as aluminum or copper, preferably aluminum. As the strip is unwound from roll Hit passes between (a pair of flanging rollers 16 and I1, roller I6 having top and bottom discs I8; Roller I6 is rotated by any suitable mechanism. (not shown). As strip [5 moves between flanging rollers 15- and I1, a narrow topflange' l9 and bottom flange '20 are formed on the top-and bottom edges of the strip 15, respectively.

In its continued movement, strip I5 passes between a reciprocating stamp 2| and a stationary platen 22. Member 2|, in the embodiment of the invention-shown in'lFigure 1, comprises a head 23, the face of which is provided with a combined cutting and deflecting member 24, and deflecting members 25, 2'6 and 21. Member 24, when it is moved into operative engagement with strip l 5, shears the strip [5 and thus produces a cutZB extending-the full width of the body portion of-strip l5, i. e.,theportion-between flanges l9 and 2B, and also deflects the portion of the strip between'this cut28 and the previous cut 29 out of the plane of the body portion of.

this strip as indicated by the reference character 30 in Figure 3. Member 25 engages a succeeding partially deflected portion of the .strip and further deflects it to the position shown in.

Figure 3 and indicated by the reference character 3!. Members 26 and 2'! effect further deflection of succeeding partially deflected portions into the positions indicated by reference characters 32 and 33, respectively. Hence the strip 15 leaving stamp 21 has in its body portion closely spaced channels 34 deflnedby vanes 35 disposed inparallel planes at .an angle of from 60 to 90 with the plane of the vbody portion of the strip, preferably an angle of at least 85, e. g., at a right angle, which vanes are produced by cutting the body portion of the strip along closely spaced lines and deflecting the material between each pair of such lines and are ingating mechanism 3i consisting of a vertically reciprocating crimping member. 38 and a cooperating platen 39 disposed to'support the underside, of the top flange l9. The particular design of crimping member employed will largely .de' pendon the construction and design of the stamp 2|. Usually, the stamp 2i and the crimping mechanism 3! are-correlated to permit the substantially continuous or step by step movement of strip l5 therethrough. to produce a flanged strip which onleaving crimping mechanism 31 has the desired number of closely spaced passages 35 defined by vanes 3.5and has a crimped flange l9 permitting the substantially .continuous or step-by step winding of this'strip on a tubular support. The crimped flange allows for the difference in the circumferential extent of the inner and outer flangev portions of the strip; the inner portion refers to that portionoflthe stripcontacting the circumferentialsurface of tube [0 and the outer portion. refers to flange portion 20. which, it will be noted, is spaced fromthe circumferential surface of tube 10 in the completed helix wound on tube i0.

The resultant strip having closely spaced pas- .sages extending through the body portion thereof defined by vanes 35 is wound onto the rotating tube I0 to form-a helix, theconvolutions-of which abut or almost abut, i. e., the convolutions are at m" least in substantially abutting relationship. commencing'operation, the leading end of the strip 15 is spot welded to tube Wand .the rotation of the tube then started. Carriage 112. hasmounted on the side thereof closest to the r0 tating tube ID a U-shaped bracket 40 having a pair of idle rollers 41 and 32 mounted for rotation on the terminal-ends 44 and 43, respectively,

of the U-shaped bracket 43. As tube i0 is rotated, carriage I2 is moved slowly on tracks I3 in a direction parallel to the axis of the rotating tube -10. Tube [0 is rotated and strip I5 is fed linearly through fianging rollers l6 and I7, stamping mechanism 2! and 22 and crimping mechanism 37 at a rate to effect Winding of the strip in the form of a helix on tube 10 with the. corrugated or crimped flange H) in contact with the brazing coating II. The idle rollers M and. 42 cause successive convolutions of the helix to abut each other, producing a closely wound helix, as shown in Figure 1.

When the desired length of tube III has been covered withthe helically wound fin, the wound tube is removed from .the supporting brace and is slipped into another tube 45 of high heat conducting material, i. e., aluminum or copper, of a diameter suchithat flange 20 forming the outer periphery of the helix wound on tube H1 1s 1n contact with the inner wall of tube 45. T03111- sure good contact between flange 20 and the inner wall of tube 45, the assembly is passed through a set of rolls which function to reduce slightly the diameter of tube 45 and thus mold a tight fit between flange 20 and the inner wall of tube 45. The unit thus produced may be placed in a rotating brace, and a strip substantially the same as that hereinabove described wound on the outer Wall of tube '45 to produce a helix 45, the convolutions of which are in abutting relationship. Each convolution of helix 46 has a corrugated or crimped flange 4'! in contact with the outer wall of tube 45, which' outer wall is provided with a brazing coating for bonding the crimped flange 41 to the outer wall of tube 45.

The assembly of tube I0, helical fin 52, tube 45 and helical fin 46 may then be subjected to elevated temperatures to soften the solder or brazing material and thereafter cooled to cause the flange 19 to bond to the outer wall of tube In, flange 20 to the inner wall of tube 45 and flange 41 to the outer wall of tube 45.

In the case of an exchanger made from an aluminum strip and wound on an aluminum tube provided with a brazing coating of an aluminumsilicon composition, the unit produced as hereinabove described is desirably heated by a stream of hot air to a temperature of about 1000 F, and then immersed in a molten salt bath at a temperature of about 1150 F. Under these conditions the brazing coating melts and upon removal of the assembly from the salt bath the molten brazing material solidifies to produce a firm bond between the fin flanges and the adjoining tubular surfaces. The resultant assembly is then Washed with hot water to remove salt adhering thereto. After this water treatment the assembly may be given an acid washing treatment, desirably employing dilute nitric acid containing a small amount of hydrofluoric acid to remove residual traces of salts and oxides, and desirably may be then washed with hot water to remove any acid which may adhere to the assembly. I

A cylindrical housing 48 is fitted over helix 45 and encloses the resultant exchanger. Housing 48 need not fit snugly on helix 4B and is generally provided with an exterior covering of insulating material to prevent heat leaks there: through.

There is thus produced an exchanger un1t consisting of a tubular support Hi desirably a hollow tube of high heat conducting material, for example, aluminum or copper, having relatively thin walls, e. g., about .12" thick and having interior integral fins 50 extending from the inner wall in a radial direction toward the center of the tube to improve heat exchange between the gaseous medium passing through tube It and that flowing through the heat exchange helix 52 disposed on this supporting tube. Tube in may have an exterior diameter of from to 4",preferably about 3". Disposed in the annular space 5i between the outer wall of tube l0 and the inner wall of tube 45 is the helix 52 made as hereinabove described having the convolutions in abutting relationship, each convolution consisting of flange portions along its opposite edges, one of which is crimped and bonded to the outer wall of the tube and the other of which is in contact with the inner wall of tube 45 and a. body portion provided with closely spaced passages formed by cutting the body portion along parallel lines extending the full depth-of the body portion and deflecting the material between each pair of lines defined by the outer wall of tube 45 and the inner wall of housing 48. Helix 45, similar to helix 52, is disposed in annulus 53, the crimped flange 4'? of helix 45 being bonded to the outer wall of tube 45 and the flange 49 being adjacent the inner wall of housing 48. Vanes 35 in each of the helices 46 and 52, in effect, produce interrupted longitudinally extending passages causing turbulent flow of the gaseous media passed therethrough.

In order to provide the large mass of high heat conducting material and high area of cold exchanger surface per unit of exchanger volume necessary for effectively recovering the cold content of the outgoing products of rectification, it is important the material of high heat conductivity of each of the helices 45 and 52 be relatively thin.

Strip I 5 from which these helices are formed may I be from 0.010" to 0.040" thick and from /2" to 2 wide. Vanes 35 may have a depth of from /ir," to and the flanges generally are from 0.005 to 0.010" wider than the vanes so that, as the several convolutions of the helical fin are brought into abutting relation with one another along the flange portions, the vanes of contiguous convolutions remain spaced with clearances of the order of 0.005 to 0.010".

Each exchanger unit hereinabove described and shown in section in Figure 4, it'will be noted, isa self-contained unit. Thus, for example, a recirculating gas may be caused to flow through the hollow supporting tube 40 and nitrogen product of rectification and air caused to flow alternately through the annuli 5| and 53, through the helices disposed in these annuli, the flow of air and nitrogen being periodically reversed through these two flow paths. In like manner the exchanger unit may be designed for the flow of air and oxygen alternately through the annuli 5! and 53. Hence, each exchanger unit may be tested under the flow conditions in which it will be used in practice to determine whether it is entirely satisfactory. 1

Desirably a plurality of exchanger units, constructed as hereinabove described, is connected with suitable headers to provide an exchanger or assembly having any desired capacity. Thus, for example, as shown in Figures 5 and 6, a top header 55 and a bottom header 5%; are connected at spaced points along the lengths thereof by a plurality of tubes 45 0f the exchanger units hereinabove described. A second top header 5? and a second base header 58 are suitably connected at spaced points by the housings 48' which, as hereinabove described, surround and are disposed concentrically to the tubes 45. A third pair of headers 59 and as are connected by tubes 5i corresponding to tubular support I5 but having a base curved portion 62 which passes through the intermediate portion 63 of housing 46; header 6B desirably is located between the second top header 5'! and the second base header 5%.

Desirably each exchanger is made in two sections, namely, an upper section 64 having a sup- I porting'tube 6! therein and the helices 46 and 52 in the annuli 5i and 53, respectively, and a lower section 55, the two sections being joined together through the intermediate portion 63, as shown in Figure 6. Lower section 65 has the top of thesupporting tube 56 therein pinched off or closed since no flow takes place through this supporting tube. The number of exchangers con 7 7, nected with the headers will depend upon. the desired capacity of the oxygen plant or other plant in which the exchangers are used.

In the operation of the exchangers of Figures and 6, oxygen, nitrogen, other rectification products, such as argon, neon, etc., air or an extraneous gas is supplied to header 59', as indicated by the full line arrow, and is circulated through the supporting tubes 6|, exiting through portions 62 and header 60.

Periodically nitrogen or oxygen rectification product flows, as indicated by full line arrows,

through header 55 and flows downwardly through.

tubes 45 through the longitudinally extending channels in the helices 52 disposed within tube 45 in indirect heat exchange relation with the recycled gas passing through tube 6land the air flowing upwardly through the longitudinally extending channels in the helices 45 in housing 48, the rectification product exiting through header 56. The air, as indicated by full line arrows, is introduced in header 58, flows upwardly through the longitudinally extending passages in the helices in the annular space 53 and exits through header 51. Any carbon dioxide or other condensibles contained in the air are deposited in the annular space 53'.

Upon reversal, which may take place every three to five minutes, the nitrogen or oxygen, as indicated by the dotted line arrows, flows through header 5? down through annular space 53 and exits through header 58. Air flows through header 55 upthrough tubes 45 through the annular space 5! and exits through header 55. Recirculated gas flows through header 59, tubes 6! into header 50, as in the preceding step of the process. Upon each reversal the oxygen or nitrogen removes the carbon dioxide and other condensibles deposited in the flow path by the air passing therethrough during the preceding step of the process.

The exchangers shown in Figures 5 and 6 are in a vertical position, the airentering the base headers and the products of rectification the top headers. If desired, the exchangers may be inverted so that the air enters the top headers and flows down and the rectification products enter the base headers and fiow up; also the exchangers may be disposed in other positions than the vertical position shown.

Where brazing is desired to improve the metalto-metal contact between the helically wound fins and the supporting tubes, the brazing material may be in the form of a coating applied to the surfaces of the tubes prior to the winding of the helical fins thereon. For instance, tube 45 may be precoated with brazing material on both the interior and exterior surfaces to bond fin 5'2 and fin 46 to these surfaces, respectively.

Also, one side of strip l5 may have a coating 6(1) of brazing material so that after being stamped, as hereinbefore described, to form the closely spaced fins, the outer faces of flanges 19v and 20 have the brazing material thereon to effect bonding to the adjacent tube surfaces. Tubes Hi and 45 may be wound. separately with fins 52 and 45, respectively, and these two completed units may then be assembled by sliding tube In with helix 5'2 thereon into tube 45. To bring flange 26 of fin 52 into close contact with the interior wall of tube 45, tube may be expanded slightl by means of hydraulic pressure. It is to be understood that brazing or soldering of the helical fins to adjacent tube surfaces is not always necessary. Frequently, satisfactory metal-to-metal contact is achieved merely by expanding a tubewith its helical fin while disposed within the tubewhich is to contact the outer periphery of the helical fin. Similarly, a 5;, tube V which encloses another tube carrying a helical fin may be passed through a set of rolls to reduce the diameter of the outer tube and thus establish good contact between the helix and the surfaces of the tubes which form the anmgnulus within which the helix is disposed.

It will be noted that this invention, eifects simultaneous formation of the helices wound on the supporting tube and the winding thereof, thus eliminating the necessity of producing ingdividual discs or-cther heat transfer elements and the disposition of-such elements within the respective iiow paths of the exchanger. Further, the spiral winding of the strip [5 on the supportingtubes greatly reduces the labor and time in- ZQpQVOlVGd' in placing. the heat exchange elements within the flow. paths, reduces, if not completely eliminates, waste ofv heat conducting material, and eliminates the necessityfor, packaging, storing and handling individual stampings or discs of 5;;gheat conducting material. The wound exchanger unit-can be observed and inspected to determine Whether it is satisfactory, the heat conducting material wound thereon being exposed to the eye. In prior type exchangers in which fins are placed 'within the tubes or discs stacked therein, this is not the case.

The feature of the exchanger of this invention involving the disposition of the oxygen or nitrogen and air flow paths in one and the same hous- 35, ing permits ready testing of each exchanger under actual operating conditions to determine whether it is gas-tight. Further, should any leak develop in operation, it is a simple matter to determine which exchanger unit is faulty and to make the necessar repair to this exchanger.

The exchanger of this invention has an exceptionally high mass of heat conducting material.

per unit of volume. Further, this heat conducting material is disposed to provide uniform heat flow paths. Thus the volutes 36 at the opposite ends of each vane are of substantially the same size and the vanes are uniformly dimensioned from end to end thereof. The turbulent flow of the gaseous media through the interrupted longitudinally extending passages, as hereinabove described, further improves the cold transfer efiiciency of the exchanger. The exchanger is therefore of exceptionally high heat transfer efiiciency. 5535 It will be understood embodiments of the invention can be made differing from the embodiment herein disclosed without departing from the scope of this invention. What is claimed is: J 1. The process of producing a heat exchange element, which comprises rotating a metal tube, feeding a thin, fiat metal strip toward the rotating tube ina plane substantially normal to said rotating tube, forming flanges on the opposite ,;longitudinal edges of said strip, cutting the portion of said strip between said flanges along closely spaced lines extending substantially the full distance between said flanges and deflecting the material between each pair of said lines to mgprovide vanes defining closely spaced, open passages in said strip, substantially the entire portion of said strip between said flanges being thus deflected out of its original plane to provide said vanes without waste and being thus utilized as 7&1 heat exchange surface, crimping one of. said,

flanges to produce closely spaced successive crimps substantially at right angles to the length of said flange, and after flanging, cutting, deflecting and crimping said strip winding said strip on said rotating tube to form a helix in which the successive convolutions are at least substantially abutting and the crimped flange of said strip is in contact with the exterior surface of said rotating tube.

2. The process of producing a heat exchange element, which comprises rotating a metal tube, feeding a thin, flat metal strip toward the rotating tube in a plane substantially normal to said rotating tube, forming flanges on the opposite longitudinal edges of said strip, cutting the portion of said strip between said flanges along closely spaced lines extending substantially the full distance between said flanges and deflecting the material between each pair of said lines to provide vanes defining closely spaced, open passages in said strip, substantially the entire portion of said strip between said flanges being thus deflected out of its original plane to provide said vanes without waste, each of said vanes extending substantially equidistantly above and below said original plane and having its opposite ends integral with said flanges, crimping one of said flanges to produce closely spaced successive crimps running the full length of said flange, thereafter winding said strip on said rotating tube to form a helix in which the successive convolutions are at least substantially abutting, the crimped flange of said strip is in contact with the exterior surface of said rotating tube and the other flange forms a quasi-cylindrical shell enclosing said rotating tube, and placing a second metal tube over said quasi-cylindrical shell with the interior surface of said second tube in contact with said quasi-cylindrical shell.

3. The process of claim 2 which includes bonding said crimped flange to the exterior surface of the first mentioned tube and said quasi-cylindrical shell to the interior surface of said second tube.

4. A heat exchange element comprising a metal tube and a helix of metal ribbon wound on the exterior surface of said tube, said ribbon comprising a crimped flange portion in contact with the exterior surface of said tube, a smooth continuous flange portion along the edge of said ribbon opposite the edge with said crimped flange portion and an integral body portion between said crimped and smooth continuous flange portions, said integral body portion having the form of a multiplicity of closely spaced vanes deflected into planes substantially at right angles to the original plane of said ribbon and each vane extending substantially equidistantly above and below said original plane, said vanes defining closely spaced, open passages through substantially all of said integral body portion, said passages being substantially at right angles to the original plane of said ribbon and extending through said helix longitudinally of said tube, and said smooth continuous flange portion forming a quasi-cylindrical shell enclosing said tube and helix.

5. The heat exchange element of claim 4 which includes a second metal tube surrounding and contacting said quasi-cylindrical shell.

6. The heat exchange element of claim 4 in which the metal tube and the metal ribbon are made of aluminum.

7. The process of claim 1 which includes bonding said crimped flange to the exterior surface of the metal tube, said metal tube and the metal ribbon being made of aluminum.

HERMAN F. BUSCI-IOW.

References Cited in the file of this patent UNITED STATES PATENTS- Number Name Date 1,340,266 Hildebrand May 18, 1920 1,584,772 Hyde May 18, 1926 1,710,579 Henshall Apr. 23, 1929 1,734,136 Kramer Nov. 5, 1929 1,798,330 Leek Mar. 31, 1931 1,854,619 Mortensen Apr. 19, 1932 1,890,185 Lucke Dec. 6, 1932. 1,932,610 Tilley Oct. 31, 1933 2,016,164 Williams Oct. 1, 1935 2,151,685 Berg Mar. 28, 1939 2,251,642 Tilley Aug. ,5, 1941 2,372,079 Gunter Mar. 20, 1945 2,549,466 Hoheisel Apr. 17, 1951 FOREIGN PATENTS Number Country Date 331,392 Great Britain July 3, 1930 46,840 France June 15, 1936 (Addition to No. 793,344) 

